Operators use different middlebox services or appliances, called inline services, such as Deep Packet Inspection (DPI), logging/metering/charging/advanced charging, Firewall, Intrusion Detection and Prevention (IDP), Network Address Translation (NAT), etc., to manage subscribers' traffic. These services have high requirements on throughput and packet inspection capabilities. They can be transparent or nontransparent to the end users. Services can be hosted on dedicated physical hardware or in virtual machines.
Service chaining may be required if the traffic needs to go through more than one inline service or service function. Moreover, if more than one chain of services is possible, the operator needs to configure the networking infrastructure efficiently so as to direct the right traffic via the right inline service path depending on service policies and requirements.